This invention relates to conveyor chains and more particularly to side-flexing chains designed to convey material along a track having arcuate sections.
Side-flexing conveyor chains are commonly used for transporting articles along a track having at least one arcuate or curved section. Under certain conditions, such as high speed and loading, these side-flexing chains have a tendency to "climb" or lift out of the curved sections of the track. This is a significant safety problem, in addition to causing poor product handling. As a result, there have been many prior art attempts to maintain conveyor chains within such curved track sections. These have included mechanical retainers such as tabs, as disclosed in U.S. Pat. No. 4,096,943 and U.S. Pat. No. 4,436,200 and beveled surfaces on the track wear sections and the chain links, such as are disclosed in U.S. Pat. No. 3,262,550. While such mechanical retainers did prevent the chain from pulling out of the curved track sections, they also prevented the chain from being lifted from the straight sections of the track. As a result, the track sections had to be removed for maintenance and cleaning, thereby complicating these procedures. Furthermore, chains with mechanical retainers still experienced some lift or tilting within the permitted tolerances between the chain and the track sections.
In order to avoid the maintenance and cleaning problems associated with mechanical retainers, an alternate method has been to magnetically maintain the conveyor chain in the curved track sections. Such magnetic retainers generally include permanent magnets positioned in or between the rails for applying a magnetic hold-down force on ferromagnetic portions of the chain links or coupling hinge pins. The magnetic approach has the advantage of allowing the chain to be easily pulled upwardly away from the corner sections of the track, since no mechanical retainer is employed. Examples of magnetic chain conveyors are disclosed in U.S. Pat. Nos. 3,581,873; 4,236,632; 4,643,298; 4,742,906; and U.S. Pat. No. 4,805,764; and U.K. patent publications 8608993, filed Apr. 14, 1986; GB 2182296A; and GB 2037690A. While magnetic retainers permit the chain to be lifted without removing track sections, the magnetic approach has several disadvantages. For example, the additional force exerted by the magnets consumes some of the chain's capacity by increasing turn factors, thereby limiting performance. In addition, the use of magnets is costly in that the corner track sections are complicated and require expensive components. Additionally, magnetic chain conveyors present a safety hazard because they provide no fail-safe mechanism to prevent the chain from leaving the corner sections other than the magnetic attraction.
Another disadvantage of magnetic retainers is that at least a portion of the conveyor chain must be formed of a magnetic material. For example, the magnetic chain conveyor disclosed in U.S. Pat. No. 4,805,764 comprises plastic chain links interconnected by hinge pins formed of a ferromagnetic material, while in U.S. Pat. No. 4,742,906, the links themselves are ferromagnetic. Such magnetic conveyor chains cannot be totally formed of plastic or Austenitic stainless steel, which possesses certain advantages over ferritic stainless and carbon steels, such as corrosion resistance and work hardening capability.